The present invention relates to an apparatus for inspecting a defect in a liquid crystal display and in particular to a surface light source prober apparatus and a inspecting method.
A conventional method of inspecting a defect in a liquid crystal display will be explained.
Firstly, in order to inspect defects which occur in a thin film transistor (TFT) array on a substrate, such as break and short of patterns and defects of TFT characteristics, probes for applying voltages and probes for detecting currents are brought into contact with D1 to Dn drain lines and G1 to Gn gate lines, respectively and application of a voltage and detection of a current is conducted and the LCD substrate is exposed to a light from a light source which is provided in a defect inspecting apparatus and TFTs are brought into a conductive state. This enables the defects to be detected if any.
As one of conventional methods of inspecting a defect in the liquid crystal display, there has been known a method of inspecting a point defect on a matrix substrate to prevent an unqualified product from being passed to the subsequent step by exposure of an active type matrix panel to a light from the upper and/or lower side thereof in a defect inspecting apparatus having a feature of detecting the potential of electrodes of pixels by irradiating one of substrates having a switching element in each pixel with an electron beam in the active matrix panel (refer to, for example, Japanese Unexamined Pat. Kokai Publication 1-292736).
Some of means for irradiating light switching elements formed on signal lines of the liquid crystal panel with a light uses a laser light (refer to, for example, Japanese Unexamined Pat. Kokai Publication 2-136761). This method remarkably reduces means for connecting the probes in the prior art inspecting apparatus for conducting an inspection by probing all signal lines.
Further, there has been known an inspecting method of irradiating thin film transistors with a visible light in an inspecting apparatus for electrically measuring the characteristics between terminals of thin film transistors to be measured, which are incorporated in the liquid crystal display (refer to, for example, Japanese Patent Kokai Publication 1-212328). In accordance with this inspecting method, the influence of insulating resistance of the probes and relay scanner per se upon the insulating resistance between terminals to be measured of TFT can be reduced. Shortening of the period of settling time of a resistance meter and high speed and precision inspection can be achieved.
However, the above-mentioned prior art methods of inspecting liquid crystal display have problems as follows:
In order to bring the amorphous silicon film (hereinafter referred to as xe2x80x9ca-Si filmxe2x80x9d) of each individual pixel of the entire LCD substrate into a conductive state, it is exposed to a light. The a-Si film may be brought into completely shortened state or inspection of line defect is possible due to differences in the intensity of light and illumination ununiformity, but more precise inspection than the line defect inspection is impossible.
Therefore, the present invention has been realized in order to overcome the above-mentioned problems. It is an object of the present invention to provide a surface light source or illuminant prober device and an method of inspecting a TFT array which is capable of detecting a point defect in an pixel area, which could not otherwise be detected, enhances the inspection precision and reduces the cost.
Further objects of the present invention will become apparent in the entire disclosure.
In order to achieve the above-mentioned object, according to an aspect of the present invention there is provided a surface prober apparatus, characterized in that said apparatus comprises means for controlling a light from a D.C. light source so that the entire surface of an LCD substrate to be inspected is irradiated with said light only at a predetermined inspection step in synchronization with an inspection process.
According to a second aspect, the apparatus comprises a shutter, opening and closing of which is controlled so that the entire surface of an LCD substrate is irradiated with a light from a D.C. light source only upon point defect inspection in an inspection process.
According to a third aspect, the apparatus comprises a D.C. light source for irradiating the entire surface of an LCD substrate to be inspected which is placed on a stage with a D.C. light; and a shutter between said D.C. light source and said LCD substrate, whereby said shutter is controlled so that the light from said D.C. light source is incident upon the entire surface of the LCD substrate to be inspected via said shutter only upon point defect inspection.
In a fourth aspect, the apparatus comprises; a D.C. light source for irradiating the entire surface of an LCD substrate to be inspected which is placed on a stage with a D.C. light; a polarization shutter which is switched for transmitting or intercepting a D.C. light from said D.C. light source, which is incident upon said LCD substrate; and probe means for applying a voltage upon a terminal of said LCD substrate to accumulate electrostatic charge on an auxiliary capacitor of a pixel of said LCD substrate and for reading the accumulated charge, wherein the shutter is controlled so that the entire surface of the LCD substrate to be inspected is uniformly irradiated with the D.C. light from said D.C. light source via said polarization filter only on point defect inspection.
According to a fifth aspect, there is provided a method of inspecting a liquid crystal display characterized in that on inspection of a TFT (thin film transistor) array by using a prober apparatus, a D.C. light having a uniform illumination which can be finely adjusted in a given range is controlled so that the TFT is irradiated with the D.C. light for point defect inspection in response to a control signal from a test device when a transistor circuit on the substrate to be inspected is turned on, and that a defect of said pixel is detected if any by detecting the amount of the leaked charge which has been accumulated in an auxiliary capacitor provided in the pixel, the leakage being caused by a short due to photoconductive effect of an amorphous silicon film residue which has not been etched in a TFT array manufacturing process.
The present invention makes it possible to detect a point defect in a display occurring due to an amorphous silicon residue and the like which has been left in a TFT array manufacturing process by irradiating a TFT array with a light from a D.C. lamp via a polarization shutter in a surface light source prober apparatus used at the final inspection step in a process for manufacturing a TFT array for liquid crystal display (LCD) using amorphous silicon (hereinafter referred to a xe2x80x9ca-Sixe2x80x9d film transistors.